It's because of lactose intolerance, means her intestine cannot digest lactose present in the milk.
Symptoms. .
Diarrhoea
Belly pain
Bloating and gas
Nausea and vomiting
Gurgling sound of intestine
You can find out lactose intolerance by LACTOSE TOLERANCE TEST (LTT) and STOOL ACIDITY TEST.
Health Tips
*Drink milk with other foods , This slows the digestive process and may lessen symptoms of lactose intolerance.
* Try goats milk
* mixing a few piece of saffron with milk help to eliminate this problem definitely.
Consult me online though this platform for further ayurveda medicines.
Thank u